A new diterpene and bioactivities of labdanes isolated from Buddleja marrubiifolia.

The new labdane [(3R*,4aR*,7S*,10aS*,10bR*)-3-ethenyl-3,4a,7,10a-tetramethyl-dodecahydro-1H-naphtho-[2,1-b]-pyran-7-yl]-methylbenzoate together with other 7 labdanes were isolated from the aerial parts of Buddleja marrubiifolia. Compound structures were elucidated by spectroscopic methods. Some compounds showed moderate to weak antimicrobial activity towards a panel of bacterial and fungal pathogens. In addition, trans-biformene (2) and ribenol acetate (8) showed to be highly cytotoxic with LC50 < 1 µg/mL, the other compounds showed moderate cytotoxic effect with a LC50 range of 6.008-15.26 µg/mL. For all isolated compounds, no inflammatory response was observed.

Vibrational Circular Dichroism: Recent Advances for the Assignment of the Absolute Configuration of Natural Products.

Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances for the AC assignment of terpenoids, aromatic compounds, alkaloids, and other natural products for the 2013-2014 period, when VCD was applied to the AC assignment of some 70 natural products. In addition, although discovered in 2012, a brief introduction to the VCD exciton coupling approach and its applications in natural products AC assignment is presented.

Optimization of the Number of Considered Conformers for the Absolute Configuration Determination of Catechin and Epicatechin Peracetates by VCD.

Epimeric catechin and epicatechin peracetates offer the possibility to explore the number of conformers needed for the absolute configuration determination without affecting the reliability of the assignment. Comparisons between experimental and DFT B3PW91/DGDZVP calculated curves showed that, in molecules.where the conformational flexibility generates a large number of conformers, it is possible to significantly reduce the number of conformers needed to generate VCD results that provide secure absolute configuration assignment.

Antidiabetic effect, antioxidant activity, and toxicity of 3',4'-Di-O-acetyl-cis-khellactone in Streptozotocin-induced diabetic rats.

Pyranocoumarins are compounds with an important pharmacological profile, such as anti-inflammatory, antioxidant, cytotoxic, antiviral, antibacterial, and hypoglycemic effects. These molecules have a widespread presence as secondary metabolites in medicinal plants used to treat Diabetes Mellitus (DM). The aim of this work was to evaluate antidiabetic activity in Streptozotocin (STZ)-induced diabetic rats and the antioxidant effects of 3',4'-Di-O-acetyl-cis-khellactone (DOAcK), as well as its toxic potential. We obtained DOAcK with an enantiomeric excess of 70% by chemical synthesis. Our results showed that this compound exerts an important antidiabetic effect: blood glucose decreased in groups treated with DOAcK by 60.9% at dose of 15mg/kg (p<0.05) compared with the diabetic control group, and demonstrated a statistically significant increase in weight gain (45.7±9.7 in the group treated with DOAcK vs. -23.0±33.1 in the group with diabetes). In a biochemical profile, DOAcK did not modify lipid metabolism and did not cause damage at the renal level. DOAcK administration increased the activities of Catalase (CAT), Glutathione Peroxidase (GPx), and Super Oxide Dismutase (SOD) to levels near those of the healthy group. Histopathological analysis exhibited morphology similar to that of the healthy group and the group treated with DOAcK. DOAcK is not mutagenic by Ames test for Salmonella typhimurium strains TA98, TA100, or TA102, and is not genotoxic by Micronucleus assay; median lethal dose (LD50) >2000mg/kg and, at this dose, no signs of toxicity or death were reported after 14days of observation. These results indicate that DOAcK can improve glucose metabolism, which may be due to the increased antioxidant activity of CAT, GPx and SOD. In addition, DOAcK is not toxic in the studies tested.

Vibrational Circular Dichroism: Recent Advances for the Assignment of the Absolute Configuration of Natural Products.

Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances for the AC assignment of terpenoids, aromatic compounds, alkaloids, and other natural products for the 2013-2014 period, when VCD was applied to the AC assignment of some 70 natural products. In addition, although discovered in 2012, a brief introduction to the VCD exciton coupling approach and its applications in natural products AC assignment is presented.

Absolute Configuration Assignment of 3',4'-di-O-acylkhellactones Using Vibrational Circular Dichroism Exciton Chirality.

The 3'R,4'R absolute configuration (AC) of the angular-type pyranocoumarins (-)-3',4'-di-O-acetylkhellactone (2), (-)-4'-O-acetyl-3'-O-angeloylkhellactone (3), (+)-3'-O-acetyl-4'-O-isobutyroylkhellactone (4), and (-)-3'-O-angeloyl-4'-O-senecioylkhellactone (5), isolated from the aerial parts of Prionosciadium thapsoides, was assigned by vibrational circular dichroism exciton chirality (VCDEC), and confirmed by comparison of their VCD frequencies with those calculated using DFT at the B3LYP/DGDZVP level. This again reveals that AC assignments based on optical rotation data are not very confident. Evaluation of Flack and Hooft parameters obtained after single-crystal X-ray diffraction analysis of 3, independently confirmed this AC.

Anti-hyperglycemic effect, inhibition of inflammatory cytokines expression, and histopathology profile in streptozotocin-induced diabetic rats treated with Arracacia tolucensis aerial-parts extracts.

ETHNOPHARMACOLOGICAL RELEVANCE: Arracacia tolucensis is a medicinal plant used in northeast of Mexico as a remedy to treat people with Diabetes mellitus (DM); however, there are no scientific studies that support this information. Thus, we evaluated the anti-hyperglycemic effect of the hexane, ethyl acetate and ethanol extracts from aerial parts in streptozotocin-induced diabetic rats. MATERIALS AND METHODS: DM was induced in Wistar male rats by single intraperitoneal injection of streptozotocin (STZ 50mg/kg). After STZ-induction, hyperglycemic rats were treated with all three extracts orally at a single dose (250 mg/kg) each 48 h for 21 days. Glibenclamide (1mg/kg) was used as a reference drug. The fasting blood glucose levels, the hematic biometry and biochemical profiles, and the inhibition of inflammatory cytokines expression were estimated. Histopathology analysis of pancreas, liver, spleen, and kidney tissue was carried out. RESULTS: Ours results showed that ethyl acetate extract decreased blood glucose levels significantly (75%, p< 0.05) when compared to diabetic rats and controlled the body weight loss; the lipids level did not change, but the enzyme levels of aspartate aminotransferase and alanine aminotransferase decreased significantly (60.83% and 66.16%, respectively, p< 0.05) and inhibited the expression of inflammatory cytokines,with respect to diabetic rats. Histopathology injury was not observed; by contrast repair of islet of Langerhans was exhibited. CONCLUSION: These results validate the use of Arracacia tolucensis as a treatment against DM and suggests it is suitable to continue studies for its safe therapeutic use.

Conformational analysis of perezone and dihydroperezone using vibrational circular dichroism.

The vibrational circular dichroism (VCD) spectra of perezone and dihydroperezone measured from CDCl(3) solutions were quite similar, suggesting analogous conformations for both molecules. Their absolute configurations were confirmed by comparison of the experimental VCD spectrum of each compound with curves generated from theoretical calculations using density functional theory (DFT) at the B3LYP/DGDZVP level of theory taking into account their conformational mobility. Conformational analysis of the 8-(R) enantiomer showed 19 low energy conformers in a 2.4 kcal/mol energy range, while for 8-(R), with the saturated side alkyl chain, 34 conformers were considered in the first 2 kcal/mol. Initial analyses were carried out using a Monte Carlo searching with the MMFF94 molecular mechanics force field, all MMFF94 conformers were geometrically optimized using DFT at the B3LYP/6-31G(d) level of theory, followed by reoptimization and calculations of their vibrational frequencies at the B3LYP/DGDZVP level. Good agreement between the theoretical 8-(R) enantiomers and experimental VCD curves were observed for both.

Myrtenal, a controversial molecule for the proper application of the CIP Sequence Rule for multiple bonds.

This communication highlights the need of building hierarchical digraphs for the unequivocal assignment of stereochemical descriptors of (-)-myrtenal, a naturally-occurring oxygenated monoterpene whose absolute configuration (AC) is sometimes misrepresented in its structural formulae. Differentiation between duplicated atoms and phantom atoms for the proper application of the sequence rules is shown to be an essential step to get a proper construction of hierarchical digraphs.

Antifeedant and cytotoxic activity of longipinane derivatives.

The polyoxygenated longipinane derivatives 1- 8 were tested as antifeedant compounds against the herbivorous insects Spodoptera littoralis, Rhopalosiphum padi, and Myzus persicae. Compounds 1-3 and 8 exhibited significant antifeedant activity against S. littoralis and M. persicae. The antifeedant activity against S. littoralis increased moderately after the C-8 hydroxy group in 3 was removed to afford 1 and increased strongly after the remaining two hydroxy groups were acetylated to afford 2. Compound 1 was active on M. persicae. Compounds 1, 3, and 4, with an unsaturated six-membered ring, exhibited an increase in post-ingestive effects on S. littoralis ranging from antifeedant in the case of 1 to toxic for compounds 3 and 4. These compounds did not have any phytotoxic effect on Lactuca sativa. When tested on a panel of tumoral cells, compounds 2 and 6 exhibited moderate selective cytotoxic effects on the p53 null lung carcinoma cells H1299, which were not affected by the drug paclitaxel. In addition, vibrational circular dichroism (VCD) was applied to the representative longipinene derivative 2 to verify its absolute configuration, and the sensitivity of the VCD methodology was evaluated by comparing spectra of the three diastereoisomers (4 R,5 S,7 R,9 R,10 R,11 R)-7,9-diacetyloxylongipin-2-en-1-one (2), (4 R,5 S,7 S,9 R,10 R,11 R)-7,9-diacetyloxylongipin-2-en-1-one, and (4 R,5 S,7 R,9 S,10 R,11 R)-7,9-diacetyloxylongipin-2-en-1-one.

Preparation and absolute configuration of (1R,4R)-(+)-3-oxo-, (1S,4S)-(-)-3-oxo- and (1R,3S,4R)-(+)-3-acetyloxy-5-oxo-1 ,8-cineole.

Enantiomerically pure (1S,4S)-(-)-3-oxo-1,8-cineole (-)-2 and (1R,4R)-(+)-3-oxo-1,8-cineole (+)-2 were prepared for the first time and their absolute configurations assigned by vibrational circular dichroism (VCD) measurements. Thus, treatment of cineole 1 with chromyl acetate gave rac-2 which after sodium borohydride reduction and acetylation provided racemic 3-endo-acetyloxy-1,8-cineole, rac-4. Enantioselective hydrolysis using porcine liver esterase (PLE) gave a mixture of 3-endo-hydroxy-1,8-cineole (-)-3 and 3-endo-acetyloxy-1,8-cineole (+)-4. After chromatographic separation, (-)-3 was oxidized to (+)-2, while (+)-4 was hydrolysed to (+)-3 and then oxidized to (-)-2. The absolute configuration of either ketone 2 was established by VCD spectroscopy in combination with density functional theory (DFT) calculations at the B3LYP/DGDZVP level of theory, from where it followed that the (+)-2 enantiomer corresponds to (1R,4R)-1,3,3-trimethyl-5-oxo-2-oxabicyclo[2.2.2]octane and the (-)-2 enantiomer to the (1S,4S) molecule which is also in agreement with the absolute configuration deduced by the Mosher method for the starting chiral alcohols. Some literature inconsistencies are clarified. In addition, the enantiomerically pure monoester (1S,3S,4R,5R)-(-)-3-acetyloxy-5-hydroxy-1,8-cineole 6 and the ketoester (1R,3S,4R)-(+)-3-acetyloxy-5-oxo-1,8-cineole 7 were prepared from meso-diacetate 5 by enantioselective asymmetrization also using PLE.

A new longipinene diester from Stevia monardifolia Kunth.

Nonpolar and medium polarity fractions from whole plant methanolic extracts of Stevia monardifolia afforded the new 7beta-angeloyloxy-8alpha-isovaleroyloxylongipin-2-en-1-one 1 along with known 7beta,8alpha-diangeloyloxylongipin-2-en-1-one 2 and 7beta,8alpha-diangeloyloxylongipinan-1-one 3. Alkaline hydrolysis of a mixture of 1 and 2 gave 7beta,8alpha-dihydroxylongipin-2-en-lone 4 which was subjected to a single crystal X-ray diffraction study. The new compound 1, which is the third 7beta,8alpha-dihydroxylongipin-2-en-1-one diester natural product isolated from a Stevia especies, was fully characterized by one- and two-dimensional NMR spectroscopy and its absolute configuration was confirmed as the 4R,5S,7S,8S,10R,11R enantiomer by vibrational circular dichroism (VCD) measurements in comparison to calculation at the B3LYP/DGDZVP level of theory.

Antifeedant and phytotoxic activity of cacalolides and eremophilanolides.

The antifeedant effect of six cacalolides and six eremophilanolides was tested against the herbivorous insects Spodoptera littoralis, Leptinotarsa decemlineata, and Myzus persicae. The test compounds included several natural products isolated from Senecio madagascariensis (14-isovaleryloxy-1,2-dehydrocacalol methyl ether, 4), S. barba-johannis (13-hydroxy-14-oxocacalohastine, 5; 13-acetyloxy-14-oxocacalohastine, 6) and S. toluccanus [6-hydroxyeuryopsin, 7; 1(10)-epoxy-6-hydroxyeuryopsin, 9; toluccanolide A, 11] and the derivatives cacalol methyl ether (1); cacalol acetate (2); 1-acetyloxy-2-methyloxy-1,2,3,4-tetradehydrocacalol acetate (3); 6-acetyloxyeuryopsin (8); 6-acetyloxy-1(10)-epoxyeuryopsin (10), and toluccanolide A acetate (12). Compound 11 and its derivative 12 exhibited moderate antifeedant activity against S. littoralis; 2, 7-10, and 12 showed strong activity against L. decemlineata, while the aphid M. persicae was moderately deterred in the presence of compounds 1, 4, 8, 10, and 12. The phytotoxic activity of 1-12 on Lactuca sativa was also evaluated. Compounds 2 and 4-12 moderately inhibited seed germination at 24 h, while compounds 1-4, 6, 9, and 10 had a significant inhibition effect on L. sativa radicle length (over 50%).

C-15-functionalized eudesmanolides from Mikania campanulata.

The aerial parts of Mikania campanulata Gardner afforded the nine new eudesmanolides (1S,4S,5S,6S,7S,10R)-1-hydroxy-15-acetoxyeudesm-11(13)-en-6,12-olide (1), (1S,4S,5S,6S,7S,10R)-1,4-dihydroxy-15-acetoxyeudesm-11(13)-en-6,12-olide (2), (1R,4S,5S,6S,7S,10R)-1,4-dihydroxy-15-acetoxyeudesm-11(13)-en-6,12-olide (3), (1R,4S,5S,6S,7S,10R)-1-hydroxy-4,15-diacetoxyeudesm-11(13)-en-6,12-olide (4), (1S,4R,5S,6S,7S,10R)-1,15-diacetoxy-4-hydroxyeudesm-11(13)-en-6,12-olide (5), (1S,5S,6S,7S,10R)-1-hydroxy-15-acetoxyeudesma-4(15),11(13)-dien-6,12-olide (6), (1S,5S,6S,7S,10R)-1,15-dihydroxyeudesma-3,11(13)-dien-6,12-olide (7a), (1S,2R,5S,6S,7S,10R)-1,2,15-trihydroxyeudesma-3,11(13)-dien-6,12-olide (8a), and (1R,6S,7S,10R)-1,15-dihydroxyeudesma-4,11(13)-dien-6,12-olide (9a), among which the last three were characterized as their corresponding peracetates (7b-9b). The structures of 1-6 and 7b-9b were elucidated using 1D and 2D NMR measurements, while that of major constituent 1 was confirmed by single-crystal X-ray diffraction analysis, and its absolute configuration evidenced from vibrational circular dichroism measurements, which were compared to results obtained from density functional theory calculations. The chemistry of the large genus Mikania is briefly analyzed.